A. Field of the Invention
This invention relates to a drill collar stabilizer used in oil well drilling operations, which can be positioned anywhere along a collar string. A stabilizer typically is equipped with exterior blades. The stabilizer is used as an aid to prevent the drill collar from sticking to the walls of the borehole. The stabilizer also prevents eccentric action of the long drill string as the borehole is drilled to greater depths.
B. Background
Traditionally, stabilizers have been made up between drill collars as the drill string has been run into the hole. This arrangement, however, has had several undesirable features. For example, it requires an extra tool joint connections between the drill collars, and these connections increase the possible points of metal fatigue in the string. It also causes variations in the drill collar stand lengths which, in turn, increase joint makeup time and detract from safe operating conditions for drilling rig personnel. Additionally, the traditional stabilizer practice requires a special bottom hole assembly which increases drilling costs and does not permit adjustment of the stabilizer along the drill collar without changing drill collar standard lengths.
The first generation of releasable drill string stabilizers solved certain problems by permitting positioning anywhere along the drill string. At the same time, however, they created other problems in that a one piece slip or wedge (segment) was placed in each end cap. This segment required an inordinate amount of force to compress and properly position the segment. The use of nonmagnetic materials, which are highly desirable in oil field work, created an additional problem in that the compressed one piece slip segment failed to regain its original shape and thus could not properly be positioned in an end cap. The specialized tools and devices which were then needed to safely compress the one piece slip segment unfortunately resulted in undesirable new labor and equipment costs. These costs were deemed undesirable by the oil well drilling operators. U.S. Pat. No. 4,258,804 describes one such one-piece slip segment.
The use of lock on stabilizers, consisting of a body with externally extending blades and two end caps for connecting to the body, has also been suggested to solve the undesirable aspects of nonstandard drill collar stand lengths. One such stabilizer is connected between the pin and box joints on a drill string by positioning an inside locking ring inside the body, and thereafter positioning an outside locking ring on each end of the body with a tapered surface facing the inside locking ring. The two end caps are used to force the rings together within the body to connect the stabilizer to the drill collar. A major difficulty encountered with this arrangement has been the inability to reuse the solid rings after once being attached. This difficulty is due to the fact that the rings become deformed when they are clamped around the drill string and thus will not release when the end cap is removed. U.S. Pat. No. 3,916,998, U.S. Pat. No. 4,101,179, and U.S. Pat. No. 4,105,262 show combinations of split rings and/or wedging clamps which have traditionally been used for attaching a stabilizer to a drill collar.
Additionally, some of the prior art devices have an excessive number of parts. Some examples of these are shown in U.S. Pat. No. 4,438,822, U.S. Pat. No. 4,131,167, and U.S. Pat. No. 4,245,709. In general, the devices render the stabilizers difficult to assemble at the well site, or they are subject to extremely complicated assembly procedures. The excessive number of parts stems from the use of wedges, slip segments, O-rings, end caps, springs, braided sleeves, belleville washers and other similar devices.